Ultra-Sensitive and Selective Ionic Sensors based on Vertical Organic Electrochemical Transistors for In-Situ Body Fluid Monitoring

Ions are ubiquitous biological and physiological regulators, while abnormal ion concentrations in human body fluids are often fingerprints of ongoing pathological states, diseases, and even organ malfunctions (such as heart or kidney failure, and dehydration). Therefore, accurate and timely detection/monitoring of various vital ion concentrations in body fluids is highly desired. Here, we demonstrate ultra-sensitive and selective ionic sensors based on vertical organic electrochemical transistors (vOECTs). By combining the advantage of high transconductance (<i>g_m</i> &gt; 0.2 S) and small footprint (&lt; 30×30 µm) of the vOECTs with specific ionic selective membranes, ultra-high sensitivities up to 13.9 mA/dec (for Na⁺), 2.2 mA/dec (for K⁺), and 187 mA/dec (for Ca²⁺) are achieved, along with decent selectivity, stability, and reproducibility. Such sensitivities are the highest values among reported ion-sensitive transistors (including ISFETs, EGOFETs, and OECTs). By integrating different vOECT-based ionic sensors in an array, in-situ monitoring of the ionic level in the externally circulated bold fluid or the dialysate during an active continuous renal replacement therapy (CRRT) is demonstrated with high accuracy and reversibility. This work demonstrates the great potential of OECT-based sensors for complex sensing scenarios.